Current techniques of manifolding and reproducing graphical representations of information, such as text and pictures (generally called “images”) involve digital-image-data processing. For example, a computer-controlled printing device or a computer display prints or displays digital image data. The image data may either be produced in digital form, or may be converted from a representation on conventional graphic media, such as paper or film, into digital image data, for example by means of a scanning device. Recent copiers are combined scanners and printers, which first scan paper-based images, convert them into digital image representations, and print the intermediate digital image representation on paper.
Typically, images to be reproduced may contain different image types, such as text and pictures. It has been recognized that the image quality of the reproduced image may be improved by a way of processing that is specific to text or pictures. For example, text typically contains more sharp contrasts than pictorial images, so that an increase in resolution may improve the image quality of text more than that of pictures.
U.S. Pat. No. 5,767,978 describes an image segmentation system able to identify different image zones (“image classes”), for example text zones, picture zones and graphic zones. Text zones are identified by determining and analyzing a ratio of strong and weak edges in a considered region in the input image. The different image zones are then processed in different ways.
U.S. Pat. No. 6,266,439 B1 describes an image processing apparatus and method in which the image is classified into text and non-text areas, wherein a text area is one containing black or nearly black text on a white or slightly colored background. The color of pixels representing black-text components in the black-text regions is then converted or “snapped” to full black in order to enhance the text data.